The invention concerns an ultrasonic applicator for the ultrasonic examination of an object, which has an extended carrying body with an applicator surface to be directed to the object. Near this application surface are a number of ultrasonic transducer elements which are arranged parallel to one another along the longitudinal axis of the carrying body. There is also a guide channel in the carrying body which extends in the direction of the application surface and is intended to receive a biopsy needle.
The removal of tissue or body fluids from organs or vessels within the body, for example, from the liver or kidneys, for diagnostic purposes by means of suitable devices, such as needles, puncture needles or biopsy needles, is a known procedure. During pregnancy, for example, amniotic fluid can be taken from the uterus for this purpose. Additionally, it is also possible to inject such substances as blood or medication into the fetal body.
In all cases it is extremely important to know the exact position of the biopsy needle in relation to the organ or vessel to be tapped, to prevent unnecessary injuries to areas, such as the placenta when tapping the uterus, or to prevent the erroneous remove of tissue from other parts of the body. In the case of injections it is correspondingly important to avoid injections that miss the target. An ultrasonic applicator used with an ultrasonic echo split-image device provides a known means of continuously checking the tap with the aid of ultrasonics. In particular, this can be accomplished with a rapid ultrasonic split-image display according to the real-time B-scan process. Such an ultrasonic applicator might consist of a carrier element which has a substantial number of ultrasonic transducer elements arranged in a row parallel to one another on the application surface. By the rapid successive activation of the individual ultrasonic transducer elements during the scanning sequence, the part of the body to be tapped is scanned line-by-line at a given section level by the generated ultrasonic beam. When an image of the ultrasonic echo pulses is formed on the screen of the display of the split-image device, a preferred split image level is selected for the direction of the tap. The biopsy needle is also clearly visible on the screen when introduced at this level, because the needle material, usually a metal, produces an easily distinguishable ultrasonic contrast with the surrounding biological tissue. Despite good visual monitoring in the scanning area aiming problems have persisted. Thus, although the movement of the needle in the tissue could indeed be followed directly with the eye on the screen of the display, this did not take place until the needle had actually arrived within the range of the ultrasonic scanning waves at the scanning section level. Until the desired range was reached the insertion process was conducted blindly.
U.S. Pat. No. 4,029,084 discloses how to avoid undesirable injuries to the tissues, due to frequent corrections of the tap, and due to delays in the tapping procedure. It states that instead of a round channel precisely adapted to the needle, the carrying body should be provided with a guide slot extending along it lengthwise for the puncture needle. The guide slot should narrow from a prescribed maximum length, which is measured off on the face opposite to the application surface of the carrying body, to a minimum slot length at the application surface itself. As a result the slot is V-shaped and located in the central part of the carrying body. Therefore, a guide channel that is closed on all sides is involved. This has the disadvantage that the ultrasonic array cannot be separated immediately from the implanted biopsy needle and removed from the patient.
It is desirable to use the same ultrasonic applicator in quick succession for various patients and biopsies, one after the other. For this purpose it is necessary for the applicator to be capable of being quickly and simply cleaned and then sterilized. One way of meeting these requirements would be to slip a sterile plastic bag over the actual ultrasonic application for each use. Then, after completion of the biopsy and before any subsequent use, this bag can be exchanged for another one. The conventional ultrasonic applicator with a central guide channel would hardly be suitable for such an operation, since the bag would be perforated when the biopsy needle was inserted. A further disadvantage is the fact that the row of ultrasonic transducer elements has a gap of a single transducer element or several transducer elements at the point on the application surface where the guide slot opens. Since individual transducer elements are missing at this point, the scanning sequence of the ultrasonic array is interrupted, and the resulting image quality precisely at the point of insertion is reduced.
An ultrasonic applicator in which the guide channel is located in the side wall rather than in the center of the extended carrying body is also commercially available. This guide channel, which accordingly opens to the side, is also frequently V-shaped. With this model, the ultrasonic applicator can be removed from the patient while the biopsy needle remains implanted. However, in this case it is also impossible to put a new sterile bag over the applicator after every patient in order to step up the number of biopsies. Actual use of the applicator has shown that in the area of the guide channel, particularly at its narrow end near the application surface, there is a folding of the material that cannot be controlled. Therefore, a risk of causing damage to the bag when the biopsy needle is put in place exists. The scanning sequence in this known applicator is also interrupted, because individual ultrasonic transducer elements are missing in the middle section, at the outlet of the guide channel.
German patent specification No. 29 06 474 discloses a method for introducing a needle guide block or guide slot element into an opening introduced in the carrying body of an applicator. The applicator contains the actual guide channel and is intended to hold the biopsy needle. Additionally, the needle guide block can be removed from the carrying body. This allows the guide channel, which comes into direct contact with the needle, to be immediately sterilized. Accordingly, hygiene and sterilization problems are largely avoided. Thus only the guide slot element, rather than the entire carrying body of the ultrasonic transducer probe, has to be sterilized prior to its use. A gas sterilization process or the like can be used and then the sterilized element can be set into the carrying body. However, even with this applicator the disadvantages mentioned above with regard to performing an increased number of biopsies and the use of a sterile bag are encountered. Furthermore, this design also has the previously described disadvantage that individual ultrasonic transducer elements are missing at the point at which the opening for the insertion of the needle guide block opens into the application surface.
In published German patent application No. 29 07 504 an ultrasonic applicator is described in which a guide device is mounted in the middle between two ultrasonic sending and receiving systems. Here, too, a number of transducer elements are missing between the two systems. These two systems are alternately operated so that a partial overlapping takes places on the screen of the display. This could also be expressed as follows: In order to be able to obtain a better view of the biopsy needle when it is inserted, in spite of the interruption of the scanning sequence that occurs at the outlet of the channel, a special program is provided here for the scanning of the ultrasonic transducer elements. However, such a special program must be provided for in the electronic system and requires relatively expensive electronic equipment. Since altered focusing is used in the area where the biopsy needle has been inserted it is possible that in this area a different tissue sample might appear on the screen, with impaired lateral resolution. In this model it also does not make sense to cover the carrying body with a sterile bag.